Drug delivery systems currently exist that supply therapeutic substances through a needle to regions of a patient's body. Such regions may include a diseased blood vessel, body cavity or organ. In the case of a diseased blood vessel, for example, the therapeutic agent may be used to treat an arterial lesion and/or to promote an angiogenic response.
In some applications, a needle may be connected to a catheter assembly to deliver the therapeutic agent deep into the body. In this application, it is difficult to determine when the needle contacts the organ, cavity wall, or vessel wall. Further, it is difficult to determine the penetration depth of the needle. In many of the applications for which a needle catheter assembly is used to deliver therapeutic agents to regions within the body, the agent must be delivered to a precise location. Accordingly, it is desirable to provide feedback that indicates when the needle contacts the cavity or vessel wall and when the needle has been inserted to a predetermined depth.